Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
1999-10-27
2001-12-04
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S043000
Reexamination Certificate
active
06327006
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device and more, precisely, to such device comprising an active substrate with a pixel transistor, TFT, thereon and a counter substrate facing the active substrate via liquid crystal therebetween.
2. Description of the Related Art
A liquid crystal display device has heretofore been known, which comprises an active substrate as prepared by forming a TFT (thin film transistor) on a substrate of, for example, glass or quartz, and a counter substrate that faces the active substrate via liquid crystal therebetween.
As a rule, the device of that type receives the rays from a light source through its counter substrate. The rays, if entering the pixel transistor in the device, will deteriorate image quality through contrast depression or flickering owing to photoelectric current leakage.
The sensitivity of polycrystalline Si (poly-Si) is not as high as compared with that of amorphous Si (a-Si). However, recent liquid crystal display devices with poly-Si-TFTs are often used in the presence of a large quantity of light, for example, as in projectors, and photoelectric current leakage is not negligible even in those devices with poly-Si-TFTs. Therefore, with the devices with poly-Si-TFTs, the problem of image quality deterioration through contrast depression or flickering owing to photoelectric current leakage comes into question.
One related technique of preventing ray penetration into the pixel transistor through the counter substrate comprises disposing a black matrix B adjacent to the counter substrate
2
, as in FIG.
1
A. As illustrated, the black matrix B acts to shield the pixel transistor from the incident rays. In this structure, however, it is impossible to prevent a part of the incident rays L
2
having scattered or reflected, from entering the pixel transistor
7
, even though the straight incident rays L
1
could be blocked by the black matrix B. To overcome this problem, the present inventors previously proposed a technique of disposing a black matrix above the transistor on the side of the active substrate
1
facing the counter substrate
2
, but not just below the counter substrate
2
to be adjacent thereto, as in FIG.
1
B. In this structure, the black matrix is nearer to the transistor, by which the incident rays going into the transistor could be reduced more effectively (see Japanese Patent Laid-Open No. 262494/1996). As illustrated in
FIG. 1B
, the incident rays L
2
having scattered or reflected could be prevented from entering the pixel transistor
7
. In this proposal, the black matrix is in two sites, both acting as a light-shielding layer.
As shown, however, a part of the passing rays L
3
, having reflected in the optical system, produces return rays (stray rays) that enter the transistor through the active substrate. In any structure, it is impossible to prevent the return rays (stray rays) L
3
from entering the transistor part
7
.
In particular, in a liquid crystal display device with a top-gate-structured or planar-structured poly-Si-TFT, the active layer of the transistor is formed on the active substrate to be the lowermost layer thereon (opposite to the counter substrate). In this, therefore, the rays running toward the active substrate directly enter the active layer of the transistor, thereby causing photoelectric current leakage.
SUMMARY OF THE INVENTION
The present invention is to solve the problems noted above, and its object is to provide a liquid crystal display device in which the incident rays having scattered and reflected and even the return rays as above are prevented from entering the transistor part and which is therefore free from the problem of photoelectric current leakage.
The liquid crystal display device of the invention comprises an active substrate with a pixel transistor TFT thereon and a counter substrate that faces the active substrate via liquid crystal therebetween, wherein a light-shielding layer is formed both adjacent to the side of the pixel transistor part that faces the counter substrate and adjacent to the side thereof that faces opposite to the counter substrate and wherein the light-shielding layer that faces the counter substrate is in at least two sites relative to the incident rays running thereinto through the counter substrate so as to block all the incident rays toward the region except the pixel openings. Depending on its overlapping condition, the light-shielding layer that is in at least two sites is so constituted that it can block all rays toward the region except the pixel openings in the device.
According to the invention, the light-shielding layer is formed both adjacent to the side of the pixel transistor part that faces the counter substrate and adjacent to the side thereof that faces opposite to the counter substrate. Therefore, as graphically shown in
FIG. 2
, even the return rays (L
3
) can be blocked by the light-shielding layer (lower light-shielding layer
5
) disposed on the side (light emitting side opposite to the counter substrate, and the device is not troubled by photoelectric current leakage to be caused by the rays erroneously entering the pixel transistor part.
REFERENCES:
patent: 4759610 (1988-07-01), Yanagisawa
patent: 4948231 (1990-08-01), Aoki et al.
patent: 5412493 (1995-05-01), Kunii et al.
patent: 5434433 (1995-07-01), Takasu et al.
patent: 5446562 (1995-08-01), Sato
patent: 5708485 (1998-01-01), Sato et al.
patent: 5754261 (1998-05-01), Lyu
patent: 5811866 (1998-09-01), Hirata
patent: 5965916 (1999-10-01), Chen
patent: 6115097 (2000-09-01), Yamazaki
patent: 6124903 (2000-09-01), Iida
patent: 8-262494 (1995-03-01), None
Abe Fumiaki
Hashimoto Yoshihiro
Hayashi Yuji
Iida Masayuki
Koike Satofumi
Rader Fishman & Grauer
Sony Corporation
Ton Toan
LandOfFree
TFT-LCD having shielding layers on TFT-substrate does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with TFT-LCD having shielding layers on TFT-substrate, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and TFT-LCD having shielding layers on TFT-substrate will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2586121